It may be useful to sense the presence of objects around a device that produces sounds and includes microphones, such as a portable computer or cellular telephone. The sensing may be based on the estimation of acoustic paths between the microphones and loudspeakers on a device, such paths being influenced by objects around the device. At a highest-level the approach is similar to sonar, as done by animals such as bats and dolphins and machines such as submarines. However, the case of interest has some particular challenges.
One challenge is that the microphones and loudspeakers already have a non-trivial, even overwhelming, “self-coupling” independent of the environment and objects around the device. Furthermore, this self-coupling occurs at frequencies and times that overlap those of the “environmental-coupling” or “object-related-coupling”.
Another challenge is to be able to do this sensing/detection by using regular signals, such as music and speech, and be able to sense/detect while other sounds in the environment, in particular ones similar to those played from the device but not originating from the loudspeakers, are present. Unlike sonar applications, no special signal-design is used. Sensing is done using signals like music and speech that are already being played out of the loudspeakers for purposes other than sensing objects, while also potentially in the presence of other similar signals not originating from the loudspeakers.
Microphones and loudspeakers may be located in the same device, and the distance of objects of interest may be similar to distances between the microphone-loudspeaker pairs. The device, such as a phone, may play speech and music on the loudspeakers. The device may be in the presence of speech and music that do not originate from the device. It may be desirable to perform environmental sensing anytime the device's loudspeakers are active, even when speech or music are currently originating from another source.
It would be desirable to detect objects in the presence of a concurrent time-frequency self-coupling that may be much larger than the environmental-coupling or object-related coupling components, as well as in the presence of other-source interference. In addition, it would be desirable to detect objects without the use of special signals by using nominal signals such as music and speech that are sent to the loudspeakers for purposes other than object sensing or detection.